Air bearing guided zoom lens for metrological measurements

ABSTRACT

A zoom lens guide system employs air bearings to reduce mechanical shift of the zoom lens components, thus reducing measurement error. The air bearings provide greater stiffness, resulting in the reduction of mechanical shift. Orifice type or porous media air bearings can be used to provide a thin film between an external surface of the bearing and an inner surface of a barrel of the system, the bearing being mounted about a lens housing within the barrel. Guide pins include feed tubes connect the air bearings to an air supply while engaging a guide slot in the barrel and a cam slot in a zoom ring to effect selective axial motion of a lens housing.

BACKGROUND AND SUMMARY

This invention relates to optical lens zoom systems, and more particularly to an improved guiding mechanism for controlling the moving parts or elements in such a lens system. It has long been customary in zoom lens systems of the type described, to employ ball bearing rollers for guiding moving parts of a zoom lens within the lens barrel. It has also been customary heretofore to employ in such lens barrel various parts which are mounted for sliding movement relative to each other to effect variation in magnification of an observed object. Lenses of the type described are frequently employed in motion picture photography and television broadcasting, which usually demand the highest of image quality. Typically such a zoom lens system includes in the lens barrel two moveable sets of lenses, the first or forward group of lenses being disposed to vary the angle of view, the second set being operative to restore the focus upon adjustment of the first group.

Among the disadvantages or prior such zoom lenses has been the difficulty encountered in accurately, and in some instances quietly, moving the respective sets of lenses. Such prior art devices also require a nearly polished finish on the inner bore wall of the lens barrel, thus contributing significantly to the manufacturing costs of the lens systems.

Accordingly, it is an object of this invention to provide an improved optical zoom lens system of the type described in which the lenses can be moved accurately and with precision not heretofore available.

Still another object of this invention is to provide an improved guiding mechanism for moving parts of an optical zoom lens system of the type described, which mechanism is easier to manufacture and is longer lasting than prior such guiding mechanisms.

Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.

In typical metrological setups, mechanical bearings are used to support and actuate a zoom lens. However, mechanical shift of the zoom components can generate an optical images shift that is an error of measurement in the optical measuring machine. Various designs of mechanical bearings have been made to attempt to overcome this problem, but the shift and resultant error remain. For example, U.S. Pat. No. 6,507,705 to Kasha, the disclosure of which is hereby incorporated by reference in its entirety, discloses one of the most accurate guiding mechanisms available for moving parts in a zoom lens system. The tubular barrel of a zoom lens mechanism has secured in the bore thereof a plurality (three in the embodiment illustrated) of elongate, circular rods which are secure to the inner peripheral surface of the barrel to extend axially thereof and in angularly spaced relation to each other. Each of a plurality of cylindrically shaped lens housings are mounted coaxially in the bore of the barrel for axial adjustment therein by means of a plurality of sets of rollers on each housing, each of which sets on each housing has rolling, point engagement with a different one of the rails. One set of rollers on each housing is urged resiliently into rolling engagement with the associated rail, while the other two sets of rollers in such housing are rotatable about axes which are fixed with respect to the associated housing. Each housing has thereon a pin which projects through a slot in the barrel and into a cam groove formed in one of two different zoom or camming rings which are rotatably mounted on the barrel. The rolling point contact between the rails and the rollers on the housing, significantly improve the accuracy and life of the mechanism. However, even this system can suffer measurement error when mechanical shift of its mechanical bearings occurs.

Embodiments offer an alternative to the mechanical bearings of the prior art. Air bearings are used in embodiments to guide a zoom lens, eliminating mechanical bearings and the related mechanical and image shift. The air bearings have higher stiffness than the mechanical bearings of the prior art, minimizing the shift of moving components in the lens system. Thus, the zoom lens system guided by an air bearing system results in greater accuracy, overcoming the problems of the prior art.

BRIEF DECRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of an elongate cylindrical lens barrel according to embodiments containing two zoom lens housings or cells and the improved mechanism for adjusting the housings longitudinally of the lens barrel, the zoom ring containing the cam slots for manipulating the lens housings being shown only fragmentarily.

FIG. 2 is an end view of the lens barrel and associated parts as seen when looking in the lower end of the lens barrel as shown in FIG. 1.

FIG. 3 is an elevation of an air bearing used in embodiments.

FIG. 4 is an elevation taken generally along the line 4-4 in FIG. 1 looking in the direction of the arrows, and illustrating the pins/air supply posts of the two lens housings mounted for adjustment in the lens barrel and the cams in which they sit according to embodiments.

FIG. 5 shows a schematic diagram of an air bearing based guiding mechanism according to embodiments.

FIG. 6 shows a more detailed schematic diagram of another air beating of embodiments.

FIG. 7 shows a schematic diagram of an air supply system for an air bearing of embodiments.

DETAILED DESCRIPTION

This description sets forth an exemplary embodiment with reference to the accompanying Figures. This exemplary embodiment is not limiting, and variations are encompassed by embodiments.

Referring now to the drawings in which like reference numerals refer to like parts, an optical gaging/metrological apparatus (not shown) of variable magnification includes a mechanism for positioning and optical component control. The optical components of embodiments can include a zoom lens optical imaging system 1 comprising a tubular lens barrel 10 with an inner sleeve portion 12 extending between flanges 13, 14 formed on opposite ends of the barrel 10. The barrel 10 includes an inner bore wall 15, and a mounting formation 16 can be included in one of the flanges 14 for mounting a component (not shown), such as a front lens. The barrel 10, inner sleeve portion 12, flanges 13, 14, and inner bore wall 15 are all preferably coaxial in embodiments.

In embodiments, at least one substantially cylindrical lens housing or cell 21 mounted for axial adjustment within the bore of barrel 10. The lenses and mountings thereof in the housing(s) 21 may be of conventional design and therefore are not described in detail herein. In a manner to be described in greater detail, each lens housing 21 is supported by an air bearing 30 for axial adjustment in the lens barrel 10. Each housing 21 can employ the same type of air bearing 30 in the same fashion, so the mounting arrangement will be described in detail in connection with only one lens housing 21 for convenience.

Rotational motion between the at least one housing 21 and the barrel 10 is undesirable, so to prevent such rotational motion, a substantially cylindrical guide pin 22 is provided for each housing 21, each pin 22 being secured at one end to one of the housings 21. The other end of each pin 22 projects slidably into an elongate guide slot 17 in the inner sleeve portion 12 of the barrel 10, the elongated slot 17 allowing motion/extension of the lens (housings) 21 longitudinally within the barrel 10. Each of the pins 22 can additionally project beyond the slot 17 in the sleeve portion 12 of the barrel 10 and into a respective cam slot 41 formed in at least one zoom ring 40 rotatably mounted on the sleeve portion 12 of the barrel 10 for effecting axial adjustment of the housing 21 within the barrel 10. In such a formation, the pin 22 becomes a cam follower, the cam slot 41 of the zoom ring 40 being the cam. The zoom ring 40 is mounted on section 12 of the lens barrel 10 for rotation relative thereto in a known manner to effect corresponding axial movements of the lens housings 21 in barrel 10. While a single zoom ring 40 is shown in the FIGS. as operating two housings 21, it should be apparent that one ring 40 could be used for each lens housing 21. Further, it should also be apparent that only one or more than two lens housings 21 could be employed with corresponding guide pins 22, air bearings 30, and cam slots 41.

As noted above, embodiments improve upon the problems associated with mechanical bearings in a zoom lens system by using air bearings 30 in place of mechanical bearings. The air bearings 30 provide a fluid movement with more accurate positioning with negligible friction losses. To accomplish this, embodiments provide that the guide pin 22 of each housing 21 is hollow, with a feed tube 31 extending therethrough. Each guide pin 22 can be connected to an air supply 60 via a supply line 61. To enhance retention of the supply line 61 on the guide pin 22, ridges 62 can be formed on the guide pin 22. Since the pin 22 can move along the longitudinal axis of the optical system in the slot 17, the air supply lines 61 are preferably flexible enough to continue supplying air at all operating positions of the system.

The feed tube 31 conducts air from the supply line 61 to the air being 30 through the guide pins 22. Embodiments preferably employ porous media type air bearings for the air bearings 30, though air bearings of the orifice type can also be employed. Where porous media air bearings are used, the feed tube 31 delivers air to the porous medium 32, which conducts the air through itself and forms an air film 33 between an external surface 34 of the air bearing 30 and the inner surface 15 of the sleeve portion 12 of the barrel 10. Where orifice type air bearings are used, the feed tube 31 delivers air to an internal distribution system that conducts the air to one or more orifices 35 to form the air film 33 between the outer surface 34 of the air bearing 30 and the inner surface 15 of the barrel 10. As is known in the bearing art, the thin film 33 of pressurized air formed in the air bearing 30 supports a load, and, in this case, provides fluid, highly controlled movement. Air bearings are different from mechanical bearings in that there is no contact between the supported and supporting surfaces during operation. The thin film of pressurized air between these solid surfaces supplies the vehicle for force transfer.

Both the porous media and orifice types of air bearings are designed so that while air is constantly dissipating from the bearing site, pressurized air is flowing into the bearing to maintain the pressure and support the solid surfaces. In embodiments, the air dissipates through the film and pressurized air flows into the bearing via the feed tube 31. Air bearings thus provide a substantially frictionless load-bearing interface between surfaces that would otherwise be in contact with each other. Since air bearings are non-contact, they avoid the traditional bearing-related problems of friction, wear, and the need for a lubricant.

The air bearing 30 of embodiments can be mounted, for example, on the external surface a respective lens housing 21. Air from the supply 60 thus travels through the supply lines 61 through the pins/cams 22 to the air bearings 30, which maintain the housings 21 substantially at a desired distance from the barrel inner surface 15. Where the air bearings 30 are of the porous medium type, embodiments can have a ring of the porous medium 32 arranged on the external surface of each housing 21 with the air film side facing the inner surface 15 of the barrel 10. To ensure proper distribution of pressurized air to the porous medium, an air conduit 36 can be formed along an inner surface of the ring of porous medium and operatively connected to the air supply 60 via the pin 22. As seen in FIG. 6, the porous medium 32 conducts the air to its outer surface to form the air film between the external surface of the bearing 30 and the inner surface 15 of the barrel 10. In embodiments where the air bearings 30 are of the orifice type, the air bearings 30 can each include an air conduit 36 and a plurality of substantially equally-spaced orifices 35 directed at the barrel 10 to form the supportive air film 33, as seen in FIG. 5. To further enhance air film distribution, more than one ring can be used.

An air supply, preferably a remote air supply 60, is fluidically connected to the air bearings via the cam followers/pins 22 extending through the slots in the barrel. The air supply in embodiments is controlled and monitored by a regulator 62 and filtered by a particle filter 63 to prevent contamination of the system. When the zoom ring 40 mounted on the barrel 10 rotates, the cam/slot 41 controls the axial position of the lens housing 21, resulting in longitudinal, reciprocal motion of the cam follower/pin 22. The longitudinal/reciprocal motion of the cam follower/pin 22 controls the magnification produced by the lens system. As seen, for example, in FIG. 7, an air supply system usable with embodiments can include a supply 60, such as a compressor, a regulator/coarse filter 62, 63, a fine filter 64, and supply lines 61.

From the foregoing it will be apparent that the present invention provides a very accurate and smooth mechanism or means for repeatedly and accurately adjusting the zoom lenses of the type carried by a housing 21 accurately to achieve the desired magnification and focus of the mechanism. The elimination of contact between the lens housings 21 and the barrel 10 not only reduces wear of the equipment during axial adjustment of the housings 21, but also reduces the effort required to make such adjustments and error introduced by contact. The air bearing arrangement of embodiments provides precision motion of the lens housings 21 without requiring the extremely hard, smooth contact surfaces and/or highly polished finish on the interior surface 15 of the barrel 10 necessary for the mechanical arrangements of the prior art.

It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. 

1. An optical metrology apparatus of variable magnification with an improved mechanism for accurate positioning and optical component control, comprising: a zoom lens optical imaging system including at least one air bearing; an air bearing control system connected to the at least one air bearing.
 2. The apparatus of claim 1 where said zoom lens optical imaging system comprises: a tubular lens barrel with an inner sleeve; at least one substantially cylindrical lens housings disposed coaxially with the barrel; and the at least one air bearing supporting the at least one lens housing and being connected to the air bearing control system.
 3. The apparatus of claim 2 further comprising a rotational motion stop between the at least one housing and the barrel, the rotational motion being arranged to prevent rotational motion of the at least one housing relative to the barrel.
 4. The apparatus of claim 3 wherein the rotational motion stop comprises a substantially cylindrical guide pin projecting from the at least one housing and through an elongate guide slot of the barrel.
 5. The apparatus of claim 4 further comprising at least one zoom ring mounted about the barrel for rotation relative thereto while being restrained against axial motion relative to the barrel, the at least one zoom ring comprising at least one respective cam slot through which the at least one guide pin projects such that rotation of the zoom ring induces axial motion of the at least one lens housing, the at least one guide pin thus comprising a cam follower.
 6. The apparatus of claim 5 wherein the guide pin includes a feed tube extending from a tip of the guide pin toward the housing and fluidically connected to the at least one air bearing.
 7. The apparatus of claim 6 wherein the at least one air bearing comprises a substantially annular bearing block surrounding the at least one lens housing and presenting its bearing surface to an inner surface of the barrel such that, when activated, an air film forms between the bearing surface and the inner surface of the barrel.
 8. The apparatus of claim 7 wherein at least one air supply conduit is formed between the at least one lens housing and the at least one bearing and the feed tube is connected to the at least one air supply conduit.
 9. The apparatus of claim 8 wherein the at least one bearing is of a porous media type, the substantially annular bearing block comprises an annulus of porous medium, and air supplied through the feed tube and air conduit passes through the porous medium to form the air film.
 10. The apparatus of claim 8 wherein the at least one bearing is of an orifice type, the substantially annular bearing block comprises an annulus of a substantially non-porous medium with at least one orifice formed therethrough, and air supplied through the feed tube and air conduit passes through the at least one orifice to form the air film.
 11. The apparatus of claim 1 wherein the air bearing control system comprises at least an air supply and respective supply lines connected to the at least one bearing, pressurized air being delivered from the air supply to the at least one bearing via the supply lines.
 12. The apparatus of claim 11 wherein the air bearing control system further comprises a regulator and at least one filter, the regulator and at least one filter being interposed in the system between the supply and the at least one bearing and being connected via the supply lines.
 13. The apparatus of claim 12 wherein the at least one filter comprises at least one of a coarse filter and a fine filter.
 14. In an optical metrology apparatus of variable magnification comprising a zoom lens optical imaging system, the zoom lens system comprising at least one substantially cylindrical lens housing arranged in a barrel and controlled by at least one zoom ring mounted about the barrel for rotation relative to the barrel while being retained against axial motion relative to the barrel, the at least one zoom ring including an elongate guide slot formed substantially parallel to a longitudinal axis of the zoom ring, an improved mechanism for accurate positioning and optical component control comprising: at least one air bearing supporting the at least one lens housing; an air bearing control system connected to and supplying pressurized air to the at least one air bearing; at least one cam formed in the zoom ring; and at least one cam follower attached to each at least one air bearing and projecting through the elongate guide slot so that the at least one lens housing can move axially within the barrel while being retained against rotation relative to the barrel.
 15. The improved mechanism of claim 14 wherein the at least one cam follower is at least one respective guide pin of each at least one bearing, the at least one guide pin projecting through the elongate guide slot and engaging the at least one cam.
 16. The improved mechanism of claim 15 wherein the at least one cam is at least one substantially helical slot formed in each at least one zoom ring and the at least one respective cam follower engages the cam such that rotation of the zoom ring induces axial motion of the respective at least one lens housing.
 17. The improved mechanism of claim 14 wherein the cam follower further comprises a feed tube extending longitudinally within the cam follower and fluidically connected to a respective at least one air bearing to deliver pressurized air from the control system to the respective at least one air bearing.
 18. The improved mechanism of claim 14 wherein the control system comprises a remote air supply controlled by a regulator and filtered by a particle filter.
 19. The improved mechanism of claim 14 wherein the at least one air bearing comprises at least one of a porous media type air bearing and an orifice type air bearing.
 20. The improved mechanism of claim 14 wherein each lens housing includes at least one respective cam follower including a respective guide pin that projects through the elongate guide slot to engage the at least one cam, the at least one cam comprising at least one substantially helical slot formed in the zoom ring such that rotation of the zoom ring induces axial motion of the lens housing via the cam follower, the guide pin including a feed tube fluidically connected to the air bearing to deliver pressurized air from the air bearing control system to the air bearing. 